The challenge of designing an energy efficient, economical residential electrical water heating system which effectively utilizes available building floor space has been heightened by the U.S. Department of Energy's recent amendment of their existing energy conservation standards for residential water heaters. In formulaic fashion, this amendment effectively requires that any residential water heater having a water storage capacity greater than fifty five gallons must incorporate therein a heat pump. While such incorporation is designed to increase the efficiency of an over-fifty five gallon water heater, installation with suitable airflow for all replacement applications may not be practical or cost effective. In view of this heightened efficiency requirement it would be desirable to provide multiple water heaters to meet the hot water requirements. It is to this goal that the present invention is primarily directed.
In representatively illustrated embodiments thereof, this invention provides specially designed water heater apparatus with features that allow for an installation comprising upper and lower vertically stacked electric individual water heaters served by a single electrical branch circuit. Each of the upper and lower water heaters has a water storage capacity not exceeding 55 gallons, and the combined water storage capacity of the upper and lower water heaters is greater than 55 gallons. The electric heating elements of the two water heaters are non-simultaneously controlled so that at no time do the two water heaters heat water at the same time.